Effect of Excitons in AlGaAs/GaAs Superlattice Solar Cells

The effect of excitonic absorption on solar cell efficiency has been investigated using solar cells with AlGaAs/GaAs superlattice active regions. Numerical calculations reveal that excitonic absorption considerably enhances the overall absorption of bulk GaAs. Excitonic absorption shows strong and sharp peaks at the absorption edge and in the energy region above the band gap. Absorption enhancement is also achieved in the AlGaAs/GaAs superlattice. The measured quantum efficiency spectra of AlGaAs/GaAs solar cells are found to be quite similar to the calculated absorption spectra considering the excitonic effect. The miniband structures of the superlattice and the electric field of the p--i--n junction enhance the dissociation of excitons and the extraction of separated carriers. These results suggest that the enhanced absorption by excitons can increase the quantum efficiency of solar cells.